At present, a thin film transistor (hereinafter, referred to as a TFT) is used favorably as a drive element in an active matrix liquid crystal display and the like. The TFT, which may have various proposed configurations, basically is configured such that a current flowing between a source electrode and a drain electrode provided in contact with a semiconductor layer is controlled by a voltage (i.e., an electric field generated by the applied voltage) applied to a gate electrode provided on the semiconductor layer via an insulating layer. Currently, the semiconductor layer constituting the TFT practically is made of a semiconductor material such as amorphous silicon and low-temperature polysilicon, which are relatively inexpensive though inferior to crystalline silicon in properties. Further, the insulating layer on which the gate electrode is provided is practically made of an insulating material such as oxide silicon and silicon nitride. However, the manufacturing process of the TFT using such a semiconductor material and an insulating material requires a large-scale device for a plasma CVD method or the like and a thin film control device for precision machining, resulting in a high manufacturing cost for the TFT. Moreover, this manufacturing process generally involves a process at temperatures higher than 350° C. Thus, there is a limit on a substrate material and the like that can be used.
In recent years, an organic semiconductor made of an organic compound as a semiconductor material that can be used for the TFT has attracted attention. As compared with the above-mentioned inorganic semiconductor of amorphous silicon, low-temperature polysilicon, or the like, the organic semiconductor allows the formation of the semiconductor layer by a low-cost and low-temperature manufacturing process such as spin coating, ink jet printing, and dip coating. Consequently, the manufacturing cost for the TFT can be reduced, and the limit on a substrate material and the like that can be used is removed. Further, due to its applicability to the low-cost and low-temperature process as mentioned above, the TFT can be formed on a flexible substrate or a large-area substrate, and accordingly it is expected to be used in a widening range of applications, for example, to a large-screen display, a sheet-like or paper-like display, and the like. However, an organic material constituting the organic TFT is likely to be deteriorated due to gas and moisture in the atmosphere. Thus, in order to use an organic material in an electronic device, it is necessary to seal the organic TFT portion by an appropriate method.
An organic electroluminescence element (hereinafter, referred to as an organic EL element) is a typical example of the electronic device using an organic material. The organic EL element also has the same problem as that of the organic TFT due to its use of an organic material. Accordingly, the life of the element is greatly dependent on a sealing technique. To solve this problem of the organic EL element, an organic EL element unit formed on a substrate has been sealed with a metal cap (Patent Document 1), or a desiccant has been provided in a vessel thereof (Patent Document 2). Further, a method is disclosed in which an organic EL element layer is sealed from both upper and lower sides with a polymer film including a barrier layer with low permeability to oxygen and water vapor (see Patent Document 3, for example). Further, a method is disclosed in which a transparent conductive film formed of a metal oxide deficient in oxygen as compared with a stoichiometric composition is formed on a surface of an organic EL element, so that moisture and oxygen are absorbed (see Patent Document 3, for example).
Although the conventional examples disclosed in Patent Documents 3, 4, and the like are intended to extend the life of the organic EL element, it is also necessary in a display apparatus (in which the organic EL is not necessarily used for a display unit) using the organic TFT as a drive element to prevent the entry of gas and moisture in the atmosphere in a like manner. However, the methods of using a metal cap as disclosed in Patent Documents 1 and 2 and the method disclosed in Patent Document 3 require an additional sealing member. As a result, the manufacturing process is increased, and a display apparatus is increased in thickness. In the method disclosed in Patent Document 4, although the organic EL element as a display element unit is protected, when the organic TFT is used, it is impossible to prevent gas and moisture in the atmosphere from entering the organic TFT unit.
As described above, to meet the demand for a sheet-like and large-screen display and an extended life, it is necessary to provide a method for protecting the organic material unit without increasing the number of constituent members.    Patent Document 1: JP 8(1996)-306955 A    Patent Document 2: JP 2002-216951 A    Patent Document 3: JP 2002-543563 A    Patent Document 4: JP 2002-237390 A